Developments in reduction and replacement of in vivo toxicity and potency tests for pertussis vaccines

The regulatory control of pertussis vaccines, as for other biological products, requires that they conform to specified standards of safety and efficacy. The current potency test for whole cell vaccines, the intracerebral mouse protection test (AMPT) is still the only such assay that has shown a correlation with protection in children. An alternative in vivo assay based on non-lethal aerosol challenge of mice has been assessed as a replacement for the current AMPT. An in vitro assay based on determination of reactive nitrogen/oxygen intermediates produced as a result of macrophage activation has also been investigated as a potential replacement for the in vivo challenge test. On the other hand, for safety testing, an enzymatic-HPLC coupled assay using a fluorescein-labelled G alpha(i3)C20 peptide to measure the enzymatic ribosylation activity of active pertussis toxin was evaluated for its suitability as a replacement for the current histamine sensitisation test (HIST). An assay for adenylate cyclase toxin (ACT)-related toxicity, based on measuring the ACT-induced oxidative burst in macrophage-like cell cultures has also been investigated. Although some questions still need to be answered in relation to the development of suitable replacements for in vivo tests of pertussis vaccines, the prospects for further improvements are promising.